1. Technical Field of the Invention
The present invention relates to an emergency call handling system for a cellular telecommunication system. In particular, the present invention is directed to forwarding user emergency information via data messages over the radio digital control channel and across the network to an emergency center when emergency voice calls cannot be set up when, for example, there exists radio voice channel congestion, network congestion, or both.
2. Background of the Invention
Providers of emergency services in North America such as in fire, police, and rescue departments are assisted in providing emergency services by the introduction of the 911 emergency number. One of the important aspects of the 911 emergency service is the public safety answering point (PSAP) system which acts as an emergency center (EC) for handling emergency calls.
All 911 calls originating from the cellular and landline telephone networks are routed to the closest PSAP for service. The PSAP also obtains the telephone number of the calling party from the network. Utilizing this calling telephone number, the PSAP accesses a remote database containing information relating telephone numbers to users' names and addresses. For a landline telephone, the billing address is the address where the telephone is located. The address information is important since often the calling party is incapable of supplying the location information or does not have sufficient time to supply this information. The location information then allows the PSAP to direct assistance to the landline telephone user involved in the emergency.
As described above, 911 calls originating from the cellular network are routed to the PSAP similarly as 911 calls originating from a landline network. However, due to the unique nature of the cellular system, other methods have also been established to aid in emergency call handling.
For example, it is known to have a 911 button, or some other pre-programmed button, on the terminal or mobile station (MS). Such a feature is disclosed in U.S. Pat. No. 5,365,570 issued to Boubelik on Nov. 15, 1994 where the MS can be dedicated to emergency use. Other known MS features to aid in emergency calls are auto-power on, remote actuation of a call, and auto dial (and redial) of a pre-programmed emergency number.
In another example, once a call is successfully set up in the cellular network, it is known to transmit on the voice channel, geocoordinates of the location where the MS is located. Such a method is disclosed in U.S. Pat. No. 5,388,147 issued to Grimes on Feb. 7, 1995. Grimes further teaches converting the geo-coordinates into conventional municipality or rural address locations when the emergency call is initiated.
While the known prior art teaches methods that facilitate the transmittal of information to the PSAP from MS's, these methods are based on the premise that the user of the cellular telephone is able to make a voice call connection to the PSAP. This voice call connection comprising of a radio voice channel and a network voice trunk connection between the mobile switching center (MSC) and the PSAP. However, it should be understood that in the cellular industry, the number of radio voice channels allocated to a particular cell site are limited and may be all in use resulting in failure to set-up a call. Also even when a radio voice channel is successfully allocated, the call may still not be set up be due to network congestion elsewhere in the cellular system.
Furthermore, the probability of failing to set-up a call increases significantly in the case of a large scale disaster like an earthquake where the network is flooded with emergency calls. This is also true for local emergencies such as a major traffic highway accident in which several subscribers may be trying to access the same cell associated with that part of the highway. In such situations the user may attempt to call the PSAP many times and still not be able to establish a voice call connection. If the terminal is low on battery power and several attempts are made to contact the PSAP, then it is possible that the terminal may run out of battery power during these attempts and the PSAP will never be informed of the user's emergency.
Accordingly, there is a need to provide a method and system of informing the PSAP of the user's emergency in the event the user of a MS is unable to obtain a voice call connection to the PSAP.